Onchocerciasis, or river blindness, is one of the most common causes of blindness worldwide. It is endemic throughout most of Sub-Saharan Africa, and is also found at several isolated foci in Central and South America. Through the efforts of the Onchocerciasis Control Programme, or OCP, onchocerciasis is no longer a significant public health problem throughout much of West Africa. Unfortunately, Nigeria has not been involved in the OCP, and Nigeria Is now the single most important focus of onchocerciasis worldwide. In the past several years, ivermectin has been shown to be a safe and effective treatment for onchocerciasis. One recent result of the discover of the effectiveness of ivermectin has been the development of several programs whose goal is to control onchocerciasis in Nigeria, by the distribution of ivermectin. The overall goal of this project is to use recently developed DNA probe technologies to detect O. volvulus to pro-Ttde epidemiological information that will be of use in most efficiently allocating the resources of ivermectin based onchocerciasis control programs in Nigeria. The specific aims of this project are to: l. Develop a facility to be based in Ibadan, Nigeria that is capable of utilizing the PCR based DNA probe based assays on a large scale basis. 2. To map the distribution of severely blinding and mild strains of O. volvulus in Nigeria. 3. To utilize recently developed PER based mass screening methods which detect O. volvulus infective larvae in vector black flies to assess the effect of long term ivermectin distribution on the transmission of severe O. volvulus in West Africa.